1. Field of the Invention
The invention relates to the field of bicycle accessories and in particular to parts for bicycles which can be used to temporarily convert two bicycles designed for single riders to a tandem tricycle built for two riders.
2. Description of the Prior Art
The connection of two single bicycles to form a bicycle built for two or what is sometimes called a tandem tricycle is well known. One typical example shown by Strong, "Tandem Tricycle," U.S. Pat. No. 4,458,908 (1984), which shows two standard bicycles connected by removing the front wheel and fork of the rear bicycle and placing an adapter on the frame of the rear bicycle. The adapter on the rear bicycle is then mounted to the rear axle of the leading bicycle. As shown in Strong, fork 68 includes two tines 70 which extend downwardly from pivot shaft 64 opposite the sides of common wheel 34. Each tine 70 is coupled to a suitable adapter 72. The adapter 72 allows lengthening of tine 70 to accommodate varying tire diameters. Tine adapter 72 may be disconnected from axle adapters 80 and axle adapters 80 are left on axle 62 of the common wheel 34 when the rear bicycle is disconnected from the tandem.
However, in order to accommodate the spread of the gear mechanism and derailer in the rear bicycle, adapter bar 72 must be mounted on the outside of tines 70 of the fork and then connected to some type of adapter 80 to the rear axle 62 of the front bicycle. This, in many cases, results in obstruction of the free motion of the adapter thereby preventing adaptation of many bicycles using derailer transmissions. Furthermore, adapters 72 and 80 are fabricated from flat plate steel and are subject to substantial stress in the tandem tricycle. Such flat plates are relatively fragile and are subject to bending or breakage. The arrangement of Strong also fails to sufficient structural rigidity.
Carswell, "Bicycle Coupling," U.S. Pat. No. 1,300,343 (1919) shows another arrangement whereby a tandem tricycle is temporarily assembled. The tines C of the fork of the rear bicycle are coupled to a coupling link 10 which is a complex forged piece having a ball bearing hub 16 into which the fork connects. Hub 16 then extends integrally downward in an arm 24 to connect to the rear axle of the front bicycle.
Again, this design is such that coupling link 10 interferes with the action of the derailer transmission of the front bicycles, and it also requires the manufacture of a costly molded link including a ball bearing hub in order to provide a strong, but swivelled connection between the two bicycles.
Hunt, "Tandem," U.S. Pat. No. 598,872 (1898) describes another tandem system in which the fork 8 of the rear bicycle is coupled directly to the axle hub of the front bicycle and is further coupled together through handlebar cables 21 and a frame connector depicted in FIGS. 1 and 3. Hunt fails to provide the rigidity of connection between the two bicycles while still allowing a degree of rotation between them through means which are easy to install and economically manufactured.
Jakobson, "Tandem Attachment for Bicycles," U.S. Pat. No. 579,982 (1897) shows another example of a tandem tricycle utilizing a frame-to-frame connection as well as a axle-to-frame in fork connection utilizing a complex linkage of rest-plates D in a lower fork C. Jakobson is difficult to assemble, manufacture and fails to provide sufficient ruggedness between the bicycles which allows for the ease of their assembly and disassembly into a tandem unit and then back into single units.
Jakobson, "Tandem Attachment for Bicycles," U.S. Pat. No. 552,907 (1896) shows another example similar to Jakobson '982 wherein two frame attachments are utilized to couple a front and rear bicycle without a fork attachment between the rear bicycle and the rear axle of the bicycle. Again, Jakobson '907 is subject to complexity, is not easily converted between tandem and single modes, and fails to provide sufficient rigidity of connection while allowing rotation between the bicycles.
What is needed is some type of connection which is inexpensive to manufacture, extremely strong and rugged, does not interfere with the action of derailers commonly used on bicycles, can easily be converted into tandem and also back to single rider configurations by the user without the need for special skills or tools, and yet provides sufficient strength and rigidity between the two bicycles to withstand abuse and provide a solid connection between the two bicycles.